Viewers are most efficient at computing the ratio between two visualized values when those values are encoded by their position on a common axis, as in a dot plot. The dominance of position encodings for this task is followed by a ranked list of other encodings including 2D area and orientation, and with intensity typically listed as the least precise encoding [1]}. There is an implicit assumption that the ranking derived from this two-value ratio judgment represents an atomic unit for visualization, so that the additional precision conveyed by position should transfer to better perceptual performance in more complex tasks.
